1. Field of the Invention
This invention relates generally to numerically-controlled machine tools, and in particular to an improved numerically-controlled machine tool including a self-balancing distance measuring system.
2. Description of the Prior Art
Numerically-controlled machine tools of the foregoing general type include means for adding partial, i.e., incremental set values, which depend on a programmed input, and partial actual values, which are generated by self-balancing distance measuring system, at defined time intervals to a set distance value and an actual distance value, and means for forming a set speed value for a controller of an input drive by the difference between the set distance value and the actual distance value, with the difference being proportional to a lag distance. The self-balancing distance measuring system in such machine tools comprises an inductive measuring transducer which is fed from the primary side of the transducer and which generates a secondary error voltage on the secondary side thereof, the magnitude and polarity of which depends upon the position of a flux vector generated on the primary side of the transducer relative to the position of a secondary winding of the transducer. The transducer further includes means for generating pulse signals which are proportional to the secondary error voltage for servoing the flux vector in the direction toward balance and measuring the actual value of the distance travelled by the secondary winding. The foregoing type of machine tool is described, for example in SINUMERIK Catalog 550 C, Part 3, October, 1974, particularly FIGS. 1 and 6, and the foregoing type of self-balancing measuring system, in Siemens-Zeitschrift 1973, pages 12 through 15, particularly FIGS. 2 and 3, in the supplement "Controls and Drives for Automating Machine Tools".
Process computers, the so-called CNC controls, are being more frequently used today for the control of machine tools. In such controls, the desired, i.e., set, distance value, which is varied in accordance with predetermined conditions, is compared with the actual distance value and a speed-command variable for a feed drive at the machine is thereby formed. Due to the operation of the sensing control, the set value and the actual value are generated from respective incremental set values and incremental actual values, i.e., the respective set and actual values are varied by an amount which has accumulated as the variance within a given time, for example 8 milliseconds. This means that only the actual value variance can be determined within the 8 milliseconds and that in the sensing intervals, an externally-created variation of the actual value is not detected as interference.